Diagnostic challenges in papillary lesions of the breast.

Papillary lesions of the breast comprise a heterogeneous group of diseases ranging from benign and atypical lesions to malignant tumours including non-invasive and invasive entities. Although diagnosis of papillary lesions featuring typical histological features is straightforward, a proportion shows overlapping features, posing diagnostic challenges. In addition to being uncommon, the excellent behaviour of papillary tumours reduces the distinguishing value of individual histological features and increases the subjectivity of interpretation of various diagnostic features. Therefore the overall categorisation, which is based on a constellation of subjective features, may vary with subsequent management implications. Concordance studies revealed that recognition of papillary carcinomas (PC) as a malignant entity by pathologists is high, but concordance of its classification into in situ and invasive disease can be problematic, as can assessment of prognostic and predictive factors in the invasive component. Identification of low nuclear grade atypia within benign papillary lesions and its classification into atypia or in situ carcinoma may also pose a diagnostic challenge. Although immunohistochemistry is helpful in evaluation of benign and atypical lesions it has a limited utility in differentiating the majority of PC as non-invasive or invasive disease. Pathologists should be aware of the various entities and the differential diagnosis of each entity, the existence of lesions with overlapping features and should follow the updated guideline recommendation for their diagnosis and management. These rare lesions usually require additional diagnostic work-up and difficult cases should trigger consensus opinion or expert referral.